CN108422824B

CN108422824B - Suspension system

Info

Publication number: CN108422824B
Application number: CN201810011013.7A
Authority: CN
Inventors: 冲村浩太郎
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2017-02-15
Filing date: 2018-01-05
Publication date: 2021-01-08
Anticipated expiration: 2038-01-05
Also published as: JP2018131055A; CN108422824A; JP6579125B2; US10343480B2; US20180229574A1; DE102017129104B4; DE102017129104A1

Abstract

The invention provides a suspension system capable of preventing unstable behavior of a vehicle when hydraulic pressure of a hydraulic cylinder on a rear wheel side is large and the vehicle is in a predetermined running state. When the hydraulic pressure of the hydraulic fluid of the rear wheel hydraulic cylinder detected by the rear wheel side hydraulic pressure detection means is equal to or greater than a predetermined threshold hydraulic pressure and a high-pressure time valve switching condition established when the travel state determination means determines that the predetermined travel state is established, the valve control device executes specific valve control for bringing the front wheel spring switching valve into a cutoff state and bringing the rear wheel spring switching valve into a communication permission state.

Description

Suspension system

Technical Field

The present invention relates to a suspension system capable of adjusting a vehicle height by a hydraulic cylinder provided between a vehicle body and a wheel.

Background

The suspension system disclosed in patent document 1 includes four hydraulic cylinders corresponding to left and right front wheels and left and right rear wheels, respectively. Each hydraulic cylinder is connected to the hydraulic oil supply and discharge device through a corresponding individual control passage.

Each individual control passage is provided with an individual control valve for opening and closing the individual control passage.

When the hydraulic oil is supplied from the hydraulic oil supply and discharge device to each hydraulic cylinder by controlling the individual control valve and the hydraulic oil supply and discharge device, the vehicle height of the vehicle mounted with the suspension system is raised. On the other hand, when the hydraulic fluid of each hydraulic cylinder is discharged to the hydraulic fluid supply and discharge device, the vehicle height of the vehicle is lowered.

The suspension system further includes four high-pressure accumulators and four low-pressure accumulators corresponding to the respective hydraulic cylinders. The spring constant of each high-pressure energy accumulator is greater than the spring constant of each low-pressure energy accumulator.

Each high-pressure accumulator is always communicated with the corresponding hydraulic cylinder via a passage for the hydraulic oil. On the other hand, each low-pressure accumulator is connected to the corresponding hydraulic cylinder via a hydraulic oil passage provided with a spring switching valve. When the spring switching valve is opened, the working oil can move between the hydraulic cylinder and the low-pressure accumulator via the passage. In other words, the hydraulic cylinder and the low-pressure accumulator communicate with each other via the passage. On the other hand, when the switching valve is closed, the working oil cannot move between the hydraulic cylinder and the low-pressure accumulator. In other words, the hydraulic cylinder and the low-pressure accumulator are no longer in communication with each other.

When the hydraulic cylinder and the low-pressure accumulator communicate with each other, the suspension stiffness (wheel rate) of the wheel corresponding to the hydraulic cylinder becomes small. On the other hand, when the hydraulic cylinder and the low-pressure accumulator are no longer communicated with each other, the suspension rigidity of the wheel corresponding to the hydraulic cylinder becomes large. That is, when the spring switching valve is opened and closed, the suspension stiffness of each wheel changes.

In this suspension system, when the vehicle is normally running, each spring switching valve is opened to reduce the suspension stiffness of each wheel. On the other hand, when the vehicle is running in a curve or running with sudden acceleration or deceleration, the spring switching valves are closed to increase the suspension stiffness of the wheels.

As is well known, the suspension stiffness refers to a spring constant at a wheel position. The suspension stiffness represents a ratio of a change amount of a ground contact load of a wheel to a change amount of an up-down distance between a wheel center of the wheel and a vehicle body (wheel bounce amount). That is, the suspension stiffness indicates the amount of change in the ground contact load of the wheel required to generate a unit wheel hop.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open No. 2008-168861

Disclosure of Invention

In general, a suspension system of a vehicle is configured such that, in an initial state, roll stiffness on a front wheel side is larger than roll stiffness on a rear wheel side to some extent. In other words, the tumble stiffness distribution on the front wheel side is larger than 50% to some extent. Therefore, when a load other than the vehicle body does not act on the vehicle and the suspension stiffness of the front wheels is the same as the suspension stiffness of the rear wheels, the steering characteristic of the vehicle is usually slightly understeer characteristic.

Generally, a luggage room is provided at the rear of the vehicle.

When the total weight of the load loaded in the trunk room of the vehicle is large, the hydraulic pressure of the hydraulic cylinder corresponding to the rear wheel is increased.

In this case, if all the spring switching valves are closed to increase the suspension stiffness of the front wheels and the suspension stiffness of the rear wheels, the suspension stiffness of the rear wheels may be excessively increased. Then, for example, the roll stiffness on the rear wheel side becomes larger than the roll stiffness on the front wheel side (that is, the roll stiffness distribution on the rear wheel side becomes larger than 50%), and the steering characteristic of the vehicle may become oversteer characteristic when the vehicle is running in a curve.

The present invention has been made to solve the above problems. That is, it is an object of the present invention to provide a suspension system capable of preventing a behavior of a vehicle from becoming unstable when a hydraulic pressure of a rear wheel side hydraulic cylinder is large and the vehicle is in a predetermined traveling state.

A suspension system according to the present invention for achieving the above object includes:

two front wheel hydraulic cylinders (20FL, 20FR) that are respectively provided between the vehicle body and the left and right front wheels (WFL, WFR) of the vehicle, that expand and contract in accordance with a change in the vertical distance between each front wheel and the vehicle body, and that move the vehicle body upward with respect to the front wheels as the hydraulic pressure of hydraulic fluid stored inside increases;

two rear wheel hydraulic cylinders (20RL, 20RR) that are respectively provided between left and right rear wheels (WRL, WRR) and the vehicle body, that extend and contract in accordance with a change in vertical distance between each rear wheel and the vehicle body, and that move the vehicle body upward with respect to the rear wheels as the hydraulic pressure of hydraulic oil stored inside increases;

a hydraulic oil supply unit (70) capable of supplying the hydraulic oil to the front wheel hydraulic cylinder and the rear wheel hydraulic cylinder while adjusting the hydraulic pressure;

four first gas springs (31) provided corresponding to the front wheel hydraulic cylinders and the rear wheel hydraulic cylinders, respectively, and having a first oil chamber (31c) that communicates with the front wheel hydraulic cylinders or the rear wheel hydraulic cylinders and is filled with hydraulic oil, and a first gas chamber (31d) filled with a gas that generates an elastic force;

four second gas springs (32) independent of the first gas springs, provided in correspondence with the respective front wheel hydraulic cylinders and the respective rear wheel hydraulic cylinders, and having a second oil chamber (32c) that can communicate with the front wheel hydraulic cylinders or the rear wheel hydraulic cylinders and is filled with hydraulic oil, and a second gas chamber (32d) filled with a gas that generates an elastic force;

two front wheel spring switching valves (62FL, 62FR) that are provided in association with the respective front wheel hydraulic cylinders and that can be switched between a communication-permitted state in which the second gas spring and the first gas spring associated with the same front wheel hydraulic cylinder are connected in series by permitting communication of the hydraulic fluid between the front wheel hydraulic cylinder and the second oil chamber associated with each other and a communication-blocked state in which the communication is blocked;

two rear wheel spring switching valves (62RL, 62RR) provided in association with the respective rear wheel hydraulic cylinders, and capable of switching between a communication permission state in which the second gas spring and the first gas spring associated with the same rear wheel hydraulic cylinder are connected in series by permitting communication of the hydraulic oil between the rear wheel hydraulic cylinder and the second oil chamber associated with each other, and a disconnection state in which the communication is disconnected;

a rear wheel side hydraulic pressure detection means (90) that detects the hydraulic pressure of the hydraulic fluid in the rear wheel hydraulic cylinder;

a travel state determination unit (100) that determines whether or not the vehicle is in a predetermined travel state; and

and a valve control device (100) that switches the front wheel spring switching valve between the communication-permitted state and the blocked state, and switches the rear wheel spring switching valve between the communication-permitted state and the blocked state.

Further, the valve control device is configured such that,

the control device sets the front wheel spring switching valve and the rear wheel spring switching valve to the blocking state when the hydraulic pressure of the hydraulic fluid of the rear wheel hydraulic cylinder detected by the rear wheel hydraulic pressure detection means is less than a predetermined threshold hydraulic pressure (Thop) and the travel state determination means determines that the travel state is the predetermined travel state,

when the hydraulic pressure of the hydraulic fluid of the rear wheel hydraulic cylinder detected by the rear wheel hydraulic pressure detection means is equal to or greater than a predetermined threshold hydraulic pressure and a high-pressure valve switching condition that is established when the travel state determination means determines that the predetermined travel state is established, specific valve control is executed to bring the front wheel spring switching valve into the blocked state and bring the rear wheel spring switching valve into the communication permission state.

For example, the running state determination means determines that the vehicle is in the predetermined running state when the vehicle is running in a curve, when the vehicle is starting suddenly, and when sudden braking is applied during high-speed running.

For example, when a heavy load is placed in a luggage room provided at the rear of a vehicle in which the suspension system of the present invention is mounted, the hydraulic pressure of the rear wheel hydraulic cylinder may become equal to or higher than a predetermined threshold hydraulic pressure.

When the vehicle is turning while the hydraulic pressure of the rear wheel hydraulic cylinder is equal to or higher than the threshold hydraulic pressure, if each switching valve is switched to the off state, the suspension stiffness of the rear wheels may be larger than the suspension stiffness of the front wheels. Then, the roll stiffness on the rear wheel side is larger than the roll stiffness on the front wheel side (i.e., the roll stiffness distribution on the rear wheel side is larger than 50%), with the result that the steering characteristic of the vehicle may become an oversteer characteristic.

However, in the present invention, when the hydraulic pressure of the hydraulic fluid in the rear wheel hydraulic cylinder is equal to or greater than the threshold hydraulic pressure and the vehicle is in the predetermined traveling state, the valve control device switches each front wheel spring switching valve to the blocking state and switches each rear wheel spring switching valve to the communication permitting state. In other words, when the valve switching condition at the time of high pressure is established, the valve control device increases the suspension rigidity of the front wheels and decreases the suspension rigidity of the rear wheels by executing the specific valve control. Therefore, the roll stiffness on the rear wheel side is hardly larger than the roll stiffness on the front wheel side.

Therefore, for example, when the vehicle is running while turning, the possibility that the steering characteristic of the vehicle becomes oversteer characteristic is low.

In one aspect of the present invention, there is provided,

a front wheel side hydraulic pressure detection means (90) for detecting the hydraulic pressure of the hydraulic fluid in the front wheel hydraulic cylinder,

the valve control device is configured to prohibit execution of the specific valve control when the high-pressure valve switching condition is satisfied when the hydraulic oil supply means supplies the hydraulic oil to the front-wheel hydraulic cylinder and the rear-wheel hydraulic cylinder and the vehicle body is moving upward relative to the front wheels and the rear wheels,

the hydraulic pressure of the hydraulic fluid in the rear wheel hydraulic cylinder when a rear wheel side hydraulic pressure ratio, which is a value obtained by dividing the hydraulic pressure of the hydraulic fluid in the rear wheel hydraulic cylinder detected by the rear wheel side hydraulic pressure detection means by the hydraulic pressure of the hydraulic fluid in the front wheel hydraulic cylinder detected by the front wheel side hydraulic pressure detection means, becomes a predetermined threshold ratio is the threshold hydraulic pressure.

The roll stiffness distribution on the front wheel side and the roll stiffness distribution on the rear wheel side have a certain correlation with the ratio between the hydraulic pressure of the hydraulic oil of the front wheel hydraulic cylinder and the hydraulic pressure of the hydraulic oil of the rear wheel hydraulic cylinder. That is, if the rear wheel side hydraulic pressure ratio, which is a value obtained by dividing the hydraulic pressure of the rear wheel hydraulic cylinder by the hydraulic pressure of the front wheel hydraulic cylinder, becomes equal to or higher than a predetermined threshold ratio, the roll stiffness on the rear wheel side may excessively increase with respect to the roll stiffness on the front wheel side.

The threshold hydraulic pressure of the present embodiment is set to the hydraulic pressure of the rear wheel hydraulic cylinder when the rear wheel side hydraulic pressure ratio becomes the threshold ratio. That is, the threshold hydraulic pressure is a variable value that changes in accordance with the hydraulic pressure of the front wheel hydraulic cylinder and the hydraulic pressure of the rear wheel hydraulic cylinder.

As described above, the threshold hydraulic pressure is a value determined based on the relationship between the roll stiffness on the front wheel side and the roll stiffness on the rear wheel side, and the hydraulic pressures of the front wheel hydraulic cylinder and the rear wheel hydraulic cylinder.

Therefore, according to the present aspect, for example, the possibility that the behavior of the vehicle becomes unstable when the vehicle is in the predetermined running state is further reduced.

Further, for example, in the case where a large-weight cargo is placed in a luggage room provided at the rear portion of the vehicle and a large number of (many) passengers are present in the vehicle, the hydraulic pressure of the hydraulic fluid of the front wheel hydraulic cylinder is (greatly) increased as compared with the case where the passenger to be present in the vehicle is only the driver. Therefore, the threshold hydraulic pressure in this case is a value larger than that in the case where the occupant is the driver only, for example.

Therefore, for example, in the case where a heavy load is placed in a luggage room provided at the rear portion of the vehicle and a plurality of (many) passengers are present in the vehicle, the hydraulic pressure of the hydraulic fluid of the rear wheel hydraulic cylinder is less likely to be equal to or higher than the threshold hydraulic pressure, as compared to the case where a heavy load is placed in a luggage room and only a driver is present in the vehicle. That is, the valve switching condition at high pressure is hard to be satisfied.

In this aspect, when the vehicle body is moving upward relative to the front wheels and the rear wheels, the specific valve control is not executed when the high-pressure-time valve switching condition is satisfied.

However, in this embodiment, the valve switching condition at the time of high pressure is hard to be satisfied. That is, when the vehicle height of the vehicle is being raised, it is difficult to set a state in which the specific valve control should be executed.

Therefore, even if the specific valve control is not executed when the vehicle body is moving upward with respect to the front wheels and the rear wheels, there is a small possibility that the behavior of the vehicle in the predetermined traveling state becomes unstable when the vehicle height of the vehicle that is performing the turning traveling is raised.

In one aspect of the present invention, there is provided,

when the high-pressure valve switching condition is satisfied when the hydraulic oil is supplied from the hydraulic oil supply means to the front-wheel hydraulic cylinder and the rear-wheel hydraulic cylinder and the vehicle body is moving upward relative to the front wheels and the rear wheels, the valve control device executes the specific valve control, and the hydraulic oil supply means is prohibited from supplying the hydraulic oil to the front-wheel hydraulic cylinder and the rear-wheel hydraulic cylinder.

In the present embodiment, when the high-pressure-time valve switching condition is satisfied while the vehicle body is moving upward relative to the front wheels and the rear wheels, the control for raising the vehicle height is prohibited, and the specific valve control is executed.

Therefore, for example, when the control for raising the vehicle height is executed and the vehicle is running while turning, the possibility that the steering characteristic of the vehicle becomes the oversteer characteristic can be reduced.

In the above description, in order to facilitate understanding of the present invention, names and/or reference numerals used in the embodiments are added to structures of the invention corresponding to the embodiments described below in parentheses. However, the components of the present invention are not limited to the embodiments defined by the reference numerals. Other objects, other features and advantages of the present invention will be readily understood from the following description of the embodiments of the present invention with reference to the accompanying drawings.

Drawings

Fig. 1 is an overall configuration diagram of a suspension system according to an embodiment of the present invention.

Fig. 2 is a timing chart showing the operation states of the valves and the pump device when the manual vehicle height control is performed.

Fig. 3 is a flowchart showing a process executed by the ECU when the automatic adjustment control is performed.

Fig. 4 is a timing chart showing the operation states of the valves and the pump device when the automatic adjustment control is performed.

Fig. 5 is a flowchart showing processing executed by the ECU when suspension stiffness switching control is performed.

Fig. 6 is a time chart showing the operating states of the valves and the hydraulic pressure sensor when the high-pressure valve switching condition is satisfied.

Fig. 7 is a timing chart showing the operating states of the valves and the hydraulic pressure sensor when the valve switching condition at the high pressure is not satisfied and the vehicle is running in a curve.

Fig. 8 is a diagram for explaining the magnitude of the threshold hydraulic pressure in the first modification of the present invention.

Fig. 9 is a flowchart similar to fig. 5 of a second modification of the present invention.

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings.

In the following description, a letter FL indicated at the end of each reference numeral indicates that the member indicated by the reference numeral is the left front wheel or a member corresponding to the left front wheel. Similarly, the letter FR attached to the end of each reference numeral indicates that the member indicated by the reference numeral is the right front wheel or a member corresponding to the right front wheel. Similarly, a letter RL marked at the end of each reference numeral indicates that the component indicated by the reference numeral is the left rear wheel or a component corresponding to the left rear wheel. Similarly, the letter RR marked at the end of each reference numeral indicates that the component indicated by the reference numeral is the right rear wheel or a component corresponding to the right rear wheel.

However, when the wheel and the member corresponding to the wheel are not required to be specified, the characters FL, FR, RL, and RR may be omitted from the reference numerals indicating these members. For example, sometimes the reference numerals of all wheels are denoted by "W".

The vehicle of the present embodiment includes a suspension system 1 shown in fig. 1.

A luggage room (not shown) is provided in a rear portion of a vehicle body of the vehicle.

The vehicle is also provided with a plurality of side doors for opening and closing a side opening of the vehicle body, and a trunk room door for opening and closing a trunk room.

The vehicle is also provided with a door open state detection unit 105 that detects the open states of the side doors and the trunk door.

The suspension system 1 includes four suspension devices 10FL, 10FR, 10RL, and 10RR, a hydraulic control circuit 50, a hydraulic oil supply/discharge device 70, and an electronic control unit 100 (hereinafter, referred to as an ECU 100).

The left front wheel WFL and the vehicle body are connected by a suspension device 10 FL. The right front wheel WFR is connected to the vehicle body by the suspension device 10 FR. The left rear wheel WRL is connected to the vehicle body by a suspension device 10 RL. The right rear wheel WRR is connected to the vehicle body by the suspension device 10 RR.

The hydraulic oil supply/discharge device 70 can supply hydraulic oil to each of the suspension devices 10FL, 10FR, 10RL, and 10RR, and can discharge hydraulic oil to each of the suspension devices 10FL, 10FR, 10RL, and 10 RR.

The hydraulic control circuit 50 is provided between each of the suspension devices 10FL, 10FR, 10RL, and 10RR and the hydraulic oil supply and discharge device 70.

The ECU100 controls the operations of the hydraulic control circuit 50 and the hydraulic oil supply and discharge device 70.

The suspension device 10 includes a wheel support member 11 (e.g., a lower arm) that supports each wheel W, and four hydraulic cylinders 20 provided between each wheel support member 11 and the vehicle body. A suspension spring (not shown) is provided between each wheel support member 11 and the vehicle body.

The suspension system 1 of the present embodiment is configured such that, in the initial state, the roll stiffness on the front wheels WFL, WFR side is slightly larger than the roll stiffness on the rear wheels WRL, WRR side. In other words, the suspension system 1 is configured such that the roll stiffness distribution ratio on the front wheels WFL, WFR side is slightly larger than 50% in the initial state. That is, the suspension system 1 is configured such that the steering characteristic of the vehicle is slightly under-steer characteristic when no load other than the vehicle acts on the vehicle and the suspension stiffness of the front wheels WFL, WFR is the same as the suspension stiffness of the rear wheels WRL, WRR.

The hydraulic cylinder 20 functions as a damper.

The respective hydraulic cylinders 20 are identical in construction to each other. Each hydraulic cylinder 20 includes a cylinder 21, a piston 22 accommodated in the cylinder 21, and a piston rod 23 having a lower end fixed to the piston 22. The axis of each hydraulic cylinder 20 (cylinder 21) is substantially parallel to the vertical direction (vertical direction).

As is well known, the piston 22 is slidable in the axial direction of the cylinder 21 with respect to the inner peripheral surface of the cylinder 21. The piston rod 23 extends in the axial direction of the cylinder 21. The lower end of the piston rod 23 is always positioned inside the cylinder 21, and the upper end of the piston rod 23 is always positioned outside the cylinder 21. The lower end of the cylinder 21 is coupled to the wheel support member 11, and the upper end of the piston rod 23 is coupled to the vehicle body. Therefore, the hydraulic cylinder 20 expands and contracts in accordance with a change in the vertical distance between the corresponding wheel support member 11 and the vehicle body.

The cylinder 21 is filled with working oil. The cylinder 21 is divided by the piston 22 into two

oil chambers

24a, 24 b. The piston 22 is provided with a communication passage 25 in the form of a through hole. The

oil chambers

24a and 24b are communicated with each other through the communication passage 25. When the piston 22 moves relative to the cylinder 21 in the vertical direction, the hydraulic oil in the cylinder 21 moves between the

oil chambers

24a and 24b via the communication passage 25. When the hydraulic oil passes through the communication passage 25, the hydraulic cylinder 20 generates a damping force corresponding to the relative movement speed of the piston 22 with respect to the cylinder 21.

In the following description, the hydraulic cylinders 20 corresponding to the front wheels WFL, WFR may be referred to as front wheel-side hydraulic cylinders 20FL, 20 FR.

Similarly, the hydraulic cylinders 20 corresponding to the rear wheels WRL, WRR may be referred to as rear wheel-side hydraulic cylinders 20RL, 20 RR.

The hydraulic control circuit 50 includes an individual supply/discharge passage 51, an individual ratio switching passage 52, an individual bypass passage 53, and a common supply/discharge passage 54. The individual supply/discharge passage 51, the individual ratio switching passage 52, the individual bypass passage 53, and the common supply/discharge passage 54 are passages for the hydraulic oil. The individual supply/discharge passage 51, the individual ratio switching passage 52, and the individual bypass passage 53 correspond to each wheel W. That is, the hydraulic control circuit 50 includes four individual supply/discharge passages 51FL, 51FR, 51RL, 51RR, four individual ratio switching passages 52FL, 52FR, 52RL, 52RR, and four individual bypass passages 53FL, 53FR, 53RL, 53 RR. The hydraulic control circuit 50 is provided with a common supply/discharge passage 54.

The oil chamber 24a of each cylinder 20 is connected to the corresponding individual supply/discharge passage 51.

The hydraulic cylinder 20 raises the piston rod 23 by the pressure (i.e., hydraulic pressure) of the hydraulic oil supplied from the corresponding individual supply/discharge passage 51. Then, the piston rod 23 raises the vehicle body relative to the corresponding wheel support member 11. The higher the hydraulic pressure of the hydraulic fluid inside the hydraulic cylinder 20, the greater the force generated by the hydraulic cylinder 20, and therefore the higher the vehicle height of the vehicle. On the other hand, when the hydraulic pressure of the hydraulic cylinder 20 decreases, the piston rod 23 decreases, and thus the vehicle height decreases.

The main accumulator 31 and the regulator valve 61 are connected to the respective supply/discharge passages 51 in this order from the cylinder 20 side.

The main accumulator 31 includes a case 31a and a partition member 31b that partitions the inside of the case 31a into two capacity change chambers. The oil chamber 31c, which is one of the capacity change chambers partitioned by the partition member 31b, is connected to the individual supply/discharge passage 51. That is, the oil chamber 31c of the main accumulator 31 is always communicated with the oil chamber 24a of the hydraulic cylinder 20. The gas chamber 31d, which is the other capacity changing chamber, is filled with a gas (e.g., nitrogen gas) as an elastic body. As is well known, the main accumulator 31 is a gas spring of a hydraulic system that generates an elastic force corresponding to the hydraulic pressure of the hydraulic cylinder 20 (i.e., the amount of protrusion of the piston rod 23 from the cylinder 21). When the volume of the oil chamber 31c of the main accumulator 31 increases due to an increase in the hydraulic pressure of the hydraulic cylinder 20, the volume of the gas chamber 31d decreases and the spring constant thereof increases. On the other hand, when the volume of the oil chamber 31c of the main accumulator 31 decreases due to the hydraulic pressure of the hydraulic cylinder 20 becoming smaller, the volume of the gas chamber 31d increases and the spring constant thereof decreases.

The regulator valve 61 is a normally closed electromagnetic on-off valve that opens and closes the individual supply/discharge passage 51.

An individual ratio switching path 52 is connected to each individual supply/discharge path 51. The connection position of each individual supply/discharge passage 51 and the corresponding individual ratio switching passage 52 is located between the regulator valve 61 and the hydraulic cylinder 20. The spring switching valve 62 and the sub accumulator 32 are connected to the individual ratio switching passage 52 in this order from the connection position side to the individual supply/discharge passage 51.

The sub accumulator 32 includes a case 32a and a partition member 32b that partitions the inside of the case 32a into two capacity change chambers. The oil chamber 32c, which is one of the capacity change chambers partitioned by the partition member 32b, is connected to the individual ratio switching passage 52. The gas chamber 32d, which is the other capacity changing chamber, is filled with a gas (e.g., nitrogen gas) as an elastic body. The sub accumulator 32 is a gas spring of a hydraulic system, like the main accumulator 31.

In the present embodiment, the spring constant of the sub accumulator 32 is smaller than the spring constant of the main accumulator 31. However, the main accumulator 31 and the sub accumulator 32 may be configured such that the spring constant of the sub accumulator 32 is larger than the spring constant of the main accumulator 31. The main accumulator 31 and the sub accumulator 32 may be configured such that the spring constants of the main accumulator 31 and the sub accumulator 32 are equal to each other.

The main accumulator 31 and the sub accumulator 32 may have any form. The main accumulator 31 and the sub accumulator 32 may be any of a bellows type, a bladder type, and a piston type, for example.

The main accumulator 31 of the present embodiment is a metal bellows accumulator excellent in gas permeation resistance at high compression pressure. The sub accumulator 32 of the present embodiment is a resin film-attached airbag accumulator having a relatively large capacity and excellent gas permeation resistance.

The spring switching valve 62 is a normally open electromagnetic opening and closing valve.

When the spring switching valve 62 is open, the hydraulic cylinder 20 communicates with the sub accumulator 32. When the spring switching valve 62 is closed, the communication between the hydraulic cylinder 20 and the sub accumulator 32 is cut off.

The four individual supply/discharge passage 51-side end portions of the common supply/discharge passage 54 are connected to the individual supply/discharge passages 51. On the other hand, the remaining end of the common supply/discharge passage 54 is connected to the hydraulic oil supply/discharge device 70. The common supply/discharge passage 54 supplies the hydraulic oil discharged from the hydraulic oil supply/discharge device 70 to each individual supply/discharge passage 51, and returns the hydraulic oil discharged from each individual supply/discharge passage 51 to the hydraulic oil supply/discharge device 70.

A main valve 64 is provided in the common supply/discharge passage 54, and the main valve 64 is a normally closed electromagnetic on-off valve. When the main valve 64 is open, each individual supply/discharge passage 51 and the hydraulic oil supply/discharge device 70 communicate with each other through the common supply/discharge passage 54. When the main valve 64 is closed, the communication between each individual supply/discharge passage 51 and the hydraulic oil supply/discharge device 70 is blocked.

The hydraulic control circuit 50 includes four individual bypass passages 53FL, 53FR, 53RL, and 53 RR. A bypass valve 63 is provided in each bypass passage 53. The bypass valve 63 is a normally closed electromagnetic on-off valve.

When the bypass valve 63 is open, the sub accumulator 32 communicates with the common supply/discharge passage 54 via the bypass valve 63 regardless of the states of the regulator valve 61 and the spring switching valve 62. Therefore, when the regulator valve 61 and the spring switching valve 62 are in the closed state and the bypass valve 63 is in the open state, each of the individual bypass passages 53 allows the working oil supplied from the common supply and discharge passage 54 to each of the individual supply and discharge passages 51 to bypass the regulator valve 61 and the spring switching valve 62 and to reach the corresponding sub accumulator 32.

The hydraulic oil supply and discharge device 70 includes a pump device 71 as a high pressure source and a reserve tank 72 as a low pressure source.

The pump device 71 includes a pump 71a and a pump motor 71b for driving the pump 71 a. The pump device 71 pumps up the working oil of the reserve tank 72 and supplies the working oil to the common supply/discharge passage 54.

The hydraulic oil supply/discharge device 70 includes a check valve 73 (check valve) and a return valve 74. The check valve 73 and the return valve 74 are provided in parallel in the hydraulic oil passage of the hydraulic oil supply and discharge device 70.

The return valve 74 selectively allows the supply of the hydraulic oil from the pump device 71 to the main valve 64 and the discharge of the hydraulic oil from the main valve 64 to the reserve tank 72.

The return valve 74 allows the working oil to flow in the passage between the main valve 64 and the reserve tank 72 at the normal time (i.e., at the time of non-operation of the pump device 71). That is, at this time, the return valve 74 allows the hydraulic oil to be discharged from the main valve 64 to the reserve tank 72.

On the other hand, when the pump device 71 is driven, the return valve 74 closes due to a differential pressure between the discharge pressure of the pump device 71 and the hydraulic pressure of the common supply/discharge passage 54. Therefore, the working oil no longer flows in the passage between the main valve 64 and the reserve tank 72. Then, the check valve 73 is opened, and therefore the hydraulic oil discharged from the pump device 71 flows toward the main valve 64.

The common supply/discharge passage 54 is also provided with a pressure sensor 90 for detecting the hydraulic pressure of the hydraulic oil flowing on the downstream side of the main valve 64 (on the side of the hydraulic cylinder 20). The pressure sensor 90 is provided in the common supply/discharge passage 54 so as to be located downstream of the main valve 64, upstream of the four bypass valves 63 (on the main valve 64 side), and upstream of the regulator valve 61.

When one of the regulator valves 61 is open and the bypass valve 63 corresponding to the regulator valve 61 is closed, the pressure sensor 90 always detects the hydraulic pressure of the hydraulic cylinder 20 corresponding to the regulator valve 61. On the other hand, when one bypass valve 63 is open and the regulator valve 61 corresponding to the bypass valve 63 is closed, the pressure sensor 90 always detects the hydraulic pressure of the sub accumulator 32 corresponding to the bypass valve 63. The pressure sensor 90 repeatedly transmits the detection result to the ECU100 every predetermined time.

The ECU100 is an abbreviation of electronic control unit. The ECU100 includes a microcomputer including a CPU and a drive circuit as main components. The microcomputer includes a plurality of memories (e.g., ROM, RAM, and backup RAM) and interfaces connected to each other via a bus. The ROM stores in advance programs executed by the CPU, data such as a lookup table (map) and constants. The RAM temporarily holds data in accordance with an instruction from the CPU. The backup RAM holds data not only when the ignition SW of the vehicle is in the on position but also when the ignition SW of the vehicle is in the off position. The interface includes an AD converter. The CPU executes a program stored in a memory (ROM) to realize various functions described later. The drive circuit includes, for example, a motor drive circuit and a solenoid valve drive circuit.

The ECU100 is connected to the regulating valve 61, the spring switching valve 62, the bypass valve 63, the main valve 64, the pump device 71 (pump motor 71b), and the door open state detecting means 105.

The ECU100 is also connected to a motion detection sensor 110 that detects a motion state of the vehicle and an operation detection sensor 120 that detects an operation by the driver.

The motion detection sensor 110 includes, for example, a vehicle speed sensor that detects a vehicle speed, a vehicle height sensor that detects a vehicle height, a vertical acceleration sensor that detects an acceleration in the vertical direction of the vehicle body, a yaw rate sensor that detects a yaw rate of the vehicle body, and a horizontal acceleration sensor that detects an acceleration in the front-rear-left-right direction of the vehicle body. The vehicle height sensor detects, as the vehicle height, the distance between each wheel support member 11 supporting each wheel W and four specific portions of the vehicle body. That is, the vehicle height sensors detect the vehicle heights at four locations corresponding to the respective wheels of the vehicle. Hereinafter, these four locations are sometimes referred to as vehicle height measurement locations.

The operation detection sensor 120 includes, for example, a stroke sensor that detects a stepping stroke of a brake pedal, a steering angle sensor that detects a steering angle of a steering wheel, and a transfer sensor that detects a shift state of a transfer.

ECU100 is also connected to a vehicle height selection switch 125 and a vehicle height adjustment off switch 130.

The body-height selection switch 125 is operated by an occupant of the vehicle. The occupant can select the target vehicle height from among the normal vehicle height, the low vehicle height, and the high vehicle height by operating the vehicle height selection switch 125. The common vehicle height is the vehicle height between the high vehicle height and the low vehicle height.

The body-height adjusting off switch 130 is operated by an occupant of the vehicle. When the body-height-adjustment off switch 130 is moved from the non-operation position (initial position) to the operation position by the occupant, the ECU100 is prohibited from executing the body-height control.

The ECU100 executes vehicle height control and suspension stiffness switching control based on detection signals detected by the motion detection sensor 110 and the operation detection sensor 120.

First, the vehicle height control will be explained.

In the present embodiment, two types of vehicle height control are executed. That is, the vehicle height control according to the present embodiment includes manual vehicle height control and automatic vehicle height control.

First, the manual vehicle height control will be explained.

The manual body-height control is performed using the body-height selection switch 125.

When the vehicle height adjustment off switch 130 is in the non-operation position, the occupant of the vehicle can select the target vehicle height from among the high vehicle height, the low vehicle height, and the normal vehicle height by operating the vehicle height selection switch 125.

Next, referring to fig. 2, the operations of the regulator valve 61, the spring switching valve 62, the bypass valve 63, the main valve 64, and the pump device 71 when the target vehicle height is set to the high vehicle height by the vehicle height selection switch 125 when the vehicle height of the vehicle is the low vehicle height will be described.

First, at time t1 in fig. 2, the ECU100 closes each spring switching valve 62 to prevent the hydraulic fluid from flowing between the hydraulic cylinder 20 and the sub accumulator 32.

Then, at time t1, ECU100 opens regulating valve 61 and main valve 64 and operates pump device 71. Then, the hydraulic oil in the reserve tank 72 is supplied to each hydraulic cylinder 20 and each main accumulator 31 via the hydraulic control circuit 50. Accordingly, the hydraulic pressure of each hydraulic cylinder 20 rises. Then, the amount of protrusion of each piston rod 23 from the corresponding cylinder 21 increases, and therefore the vehicle height at each vehicle height measurement location rises. At this time, since the bypass valve 63 is closed, the hydraulic oil does not flow to each sub accumulator 32, and therefore the hydraulic pressure of each sub accumulator 32 does not increase.

The ECU100 maintains the control valves 61 and the main valve 64 in the open state, the bypass valves 63 in the closed state, and the pump device 71 in the operating state until the vehicle height at each vehicle height measurement location detected by the vehicle height sensor becomes the target vehicle height, i.e., the high vehicle height.

When the vehicle height at each vehicle height measurement location detected by the vehicle height sensor at time t2 becomes the target vehicle height, that is, the high vehicle height, the ECU100 acquires the hydraulic pressure of the hydraulic oil detected by the pressure sensor 90. At this time, the hydraulic pressure detected by the pressure sensor 90 is equal to the hydraulic pressure of the hydraulic fluid in each hydraulic cylinder 20. The hydraulic pressure detected by the pressure sensor 90 at this time is referred to as the vehicle-height-adjustment completion pressure PO-U. The vehicle-height adjustment completion pressure PO-U is recorded in the memory of the ECU 100.

Next, the ECU100 switches the regulator valve 61 to the closed state and the bypass valve 63 to the open state at time t 2. Then, the ECU100 maintains the main valve 64 in the open state and maintains the pump device 71 in the operating state. Then, the hydraulic oil flowing from the reserve tank 72 to the common supply/discharge passage 54 flows to the sub accumulators 32 through the respective bypass passages 53, and therefore the hydraulic pressure of the sub accumulators 32 rises.

Then, the ECU100 acquires the hydraulic pressure of the hydraulic oil measured by the pressure sensor 90. At this time, the hydraulic pressure detected by the pressure sensor 90 is equal to the hydraulic pressure of the hydraulic oil in each sub accumulator 32.

When the hydraulic pressure of the hydraulic oil in each sub accumulator 32 detected by the pressure sensor 90 at time t3 is equal to the vehicle height adjustment completion pressure PO-U, the ECU100 switches each bypass valve 63 from the open state to the closed state and stops the pump device 71.

Then, the ECU100 switches each spring switching valve 62 from the closed state to the open state. Thereby, each hydraulic cylinder 20 communicates with the corresponding sub accumulator 32. Then, as described later, the suspension rigidity of each wheel W is set small.

Since the hydraulic pressure of each hydraulic cylinder 20 and the hydraulic pressure of the corresponding sub accumulator 32 are equal to each other at time t3, the hydraulic oil does not move from each hydraulic cylinder 20 to the corresponding sub accumulator 32 when each spring switching valve 62 is opened. That is, at this time, the projecting amount of each piston rod 23 with respect to the corresponding cylinder 21 does not change (does not decrease), and therefore the vehicle height at each vehicle height measurement portion is maintained at the high vehicle height.

At time t4, ECU100 switches main valve 64 to the closed state to end the manual vehicle height control.

Note that, even in the case of lowering the target vehicle height, the manual vehicle height control is executed by the same procedure as in the case of raising the target vehicle height.

In this case, however, the pump device 71 is maintained in the non-operating state while the manual vehicle height control is being executed.

Next, the automatic vehicle height control will be described.

The automatic vehicle height control comprises automatic adjustment control and vehicle speed corresponding automatic control.

The automatic adjustment control will be explained first.

The ECU100 determines, for each predetermined time, whether or not the vehicle height at each vehicle height measurement location deviates from the target vehicle height by a predetermined amount or more, using the detection value of the vehicle height sensor.

The automatic adjustment control is a control for substantially returning the vehicle height at each vehicle height measurement portion to the target vehicle height when the number of times the vehicle height at each vehicle height measurement portion deviates from the target vehicle height by a predetermined amount or more within a predetermined time is equal to or more than a predetermined number of times when the vehicle is stopped or running. For example, after the vehicle height is adjusted to the target vehicle height set by the vehicle height selection switch 125 by manual vehicle height control, if the total weight of all occupants and/or the total weight of the cargo loaded in the luggage room is larger than that before the vehicle height adjustment, the vehicle height at each vehicle height measurement location may be lowered from the target vehicle height. In such a case, the automatic adjustment control is executed.

The automatic adjustment control according to the present embodiment will be described below with reference to fig. 3 and 4.

When the ignition SW of the vehicle is switched from off to on by an operation of an ignition key, not shown, the ECU100 repeatedly executes the routine shown in the flowchart of fig. 3 every time a predetermined time elapses.

As is apparent from fig. 4, the ECU100 maintains the spring switching valve 62 in the open state when the automatic adjustment control is executed.

First, in step 301, the ECU100 determines whether or not the actual vehicle height at each vehicle height measurement location at the present time is substantially deviated from the target vehicle height. More specifically, ECU100 determines whether or not the number of times that the difference between the actual vehicle height and the target vehicle height is larger than a predetermined threshold error recorded in the memory within a predetermined time is equal to or larger than a predetermined number of times.

For example, when the ECU100 determines yes in step 301 at time t5 of fig. 4, the ECU100 proceeds to step 302. Then, for example, at time t5, ECU100 opens each of the closed regulating valves 61 and opens the closed main valve 64.

The ECU100 having finished the processing of step 302 proceeds to step 303 to operate the pump device 71 at time t5, for example.

Then, the hydraulic oil flowing from the reserve tank 72 to the common supply/discharge passage 54 flows to the hydraulic cylinders 20 through the individual bypass passages 53 and the individual supply/discharge passages 51. Therefore, the hydraulic pressure of each hydraulic cylinder 20 rises, and the vehicle height at each vehicle height measurement location rises.

The ECU100 having finished the process of step 303 proceeds to step 304 to determine whether or not the difference between the vehicle height and the target vehicle height is equal to or less than a threshold error.

For example, when the ECU100 determines yes in step 304 at time t6 of fig. 4, the ECU100 proceeds to step 305. Then, the ECU100 stops the pump device 71 at time t6, for example.

The ECU100 having finished the processing of step 305 proceeds to step 306, and closes each of the control valves 61 in the open state and closes the main valve 64 in the open state at time t6, for example.

As a result, the vehicle height of the vehicle is maintained at the vehicle height at which ECU100 determines yes at step 304.

The ECU100 having finished the process of step 306 temporarily ends the process of this routine.

If no is determined in step 301, the ECU100 once ends the processing of this routine.

Next, vehicle speed-based automatic control will be described.

For example, when the occupant selects the target vehicle height as the low vehicle height or the high vehicle height, the ECU100 changes the target vehicle height to the normal vehicle height when the vehicle speed of the vehicle is higher than a predetermined first threshold speed. Then, for example, when the vehicle speed of the vehicle is higher than a predetermined second threshold speed, the ECU100 changes the target vehicle height to a preset high-speed-running low vehicle height. When the transfer detected by the transfer sensor is set to the L4 range (off-road travel range), the ECU100 switches the target vehicle height to the high vehicle height when the vehicle speed of the vehicle is equal to or higher than a predetermined third threshold vehicle speed. These controls are vehicle speed-corresponding automatic controls.

The vehicle speed-dependent automatic control is executed by the ECU100 switching the operating states of the regulator valve 61, the spring switching valve 62, the bypass valve 63, the main valve 64, and the pump device 71 in the same manner as the automatic adjustment control. That is, the vehicle speed-dependent automatic control is executed by the ECU100 controlling the regulator valve 61, the spring switching valve 62, the bypass valve 63, the main valve 64, and the pump device 71 in accordance with the processes of steps 302 to 305 of the flowchart of fig. 3.

Next, suspension stiffness switching control will be explained.

In the present embodiment, when the suspension stiffness is switched, communication between the corresponding sub accumulator 32 and the hydraulic cylinder 20 is permitted or prohibited. That is, the ECU100 controls the opening and closing of the spring switching valve 62 to permit or prohibit communication between the sub accumulator 32 and the hydraulic cylinder 20.

When the sub accumulator 32 communicates with the hydraulic cylinder 20, the main accumulator 31 and the sub accumulator 32 are connected in series. Therefore, the spring constant of one gas spring when the main accumulator 31 and the sub accumulator 32 are regarded as one gas spring (when handled as one gas spring) is smaller than the spring constant of the main accumulator 31 alone.

In other words, when the communication between the sub accumulator 32 and the hydraulic cylinder 20 is blocked by closing the spring switching valve 62, the suspension stiffness of the wheel W corresponding to the hydraulic cylinder 20 increases. On the other hand, when the sub accumulator 32 communicates with the hydraulic cylinder 20 by opening the spring switching valve 62, the suspension stiffness of the wheel W corresponding to the hydraulic cylinder 20 decreases.

For example, when the vehicle is in a predetermined running state described later, the ECU100 closes all the spring switching valves 62 except for a case where a high-pressure valve switching condition described later is satisfied. Then, the flow of the hydraulic oil between each hydraulic cylinder 20 and each sub accumulator 32 is shut off, and the suspension stiffness of each wheel W increases.

In the present embodiment, ECU100 determines that the vehicle is in the predetermined running state based on the detection result of motion detection sensor 110 when the vehicle is running in a curve, when the vehicle is starting in an emergency, or when the emergency brake is applied during high-speed running.

For example, the vehicle performs a rolling motion while running in a curve. However, by increasing the suspension rigidity of each wheel W, the amount of rolling motion of the vehicle body can be reduced.

On the other hand, for example, when the vehicle is not in the predetermined running state, the ECU100 opens all the spring switching valves 62 to communicate the hydraulic cylinders 20 with the sub accumulators 32. As a result, the suspension stiffness of each wheel W is reduced, and the ride quality of the vehicle is improved.

However, in the present embodiment, the ECU100 cannot execute the suspension rigidity switching control when the vehicle height is changing due to the automatic vehicle height control. On the other hand, if the predetermined condition set for each of the automatic vehicle height controls is satisfied while the suspension rigidity is changing due to the suspension rigidity switching control, the ECU100 interrupts the suspension rigidity switching control and executes the automatic vehicle height control.

In addition, when at least one of the side door and the trunk door is opened, the total weight of all the passengers and/or the total weight of the cargo loaded in the trunk room may change before the doors are closed. Therefore, the ECU100 does not perform the suspension rigidity switching control regardless of which door is in the open state.

When the vehicle height control and the suspension stiffness switching control are executed, the ECU100 may control the suspension devices 10FL, 10FR, 10RL, and 10RR simultaneously, or may control the suspension devices 10FL, 10FR, 10RL, and 10RR sequentially one by one.

When the total weight of the load loaded in the luggage room provided at the rear portion of the vehicle is large, the hydraulic pressure of the rear wheel side hydraulic cylinders 20RL and 20RR becomes large. Then, the hydraulic pressures of the rear wheel side hydraulic cylinders 20RL and 20RR may become equal to or higher than a predetermined threshold hydraulic pressure Thop recorded in the memory of the ECU 100.

When the hydraulic pressure of the rear wheel side hydraulic cylinders 20RL, 20RR is equal to or greater than the threshold hydraulic pressure Thop, if all the spring switching valves 62 are closed and the suspension stiffness of the front wheels WFL, WFR and the suspension stiffness of the rear wheels WRL, WRR are increased, the suspension stiffness of the rear wheels WRL, WRR becomes excessively large. Therefore, the suspension stiffness of each rear wheel WRL, WRR may be greater than the suspension stiffness of each front wheel WFL, WFR. Therefore, the roll stiffness on the rear wheels WRL, WRR side becomes larger than the roll stiffness on the front wheels WFL, WFR side, and as a result, the steering characteristic of the vehicle may become oversteer characteristic, for example, when the vehicle is turning.

Further, when the suspension stiffness of each rear wheel WRL, WRR is greater than the suspension stiffness of each front wheel WFL, WFR, the behavior of the vehicle may become unstable when the vehicle is suddenly started or when the vehicle is suddenly braked when traveling at a high speed.

Therefore, in the present embodiment, the suspension stiffness switching control mode when the vehicle is in the predetermined traveling state is changed depending on whether or not the hydraulic pressure of the rear wheel side hydraulic cylinders 20RL, 20RR is equal to or higher than the threshold hydraulic pressure Thop.

Hereinafter, the suspension stiffness switching control according to the present embodiment will be described in detail with reference to fig. 5 to 7.

When the ignition SW of the vehicle is switched from off to on by the operation of the ignition key, the ECU100 repeatedly executes the routine shown in the flowchart of fig. 5 every time a predetermined time elapses.

As is apparent from fig. 6 and 7, the ECU100 maintains the bypass valve 63 in the closed state when the suspension stiffness switching control is executed.

First, the ECU100 determines in step 501 whether the automatic vehicle-height control is being executed at the present time.

Then, the ECU100 determines in step 501 whether or not at least one of the side door and the trunk door is in an open state at the present time based on information from the door open state detection unit 105.

If yes is determined in step 501, the ECU100 proceeds to step 510 to open all the spring switching valves 62. When all the spring switching valves 62 are in the open state at the processing time of step 501, the ECU100 maintains all the spring switching valves 62 in the open state at step 510.

The ECU100 having finished the process of step 510 temporarily ends the process of this routine.

If it is determined as no in step 501, the ECU100 proceeds to step 502, and switches the control valves 61RL and 61RR corresponding to the rear wheels WRL and WRR from the closed state to the open state at time t7, for example, as shown in fig. 6 and 7.

The ECU100 having finished the process of step 502 proceeds to step 503, and for example, at time t7, the ECU100 acquires the hydraulic pressures of the rear wheel side hydraulic cylinders 20RL and 20RR measured by the pressure sensor 90 from the pressure sensor 90.

Further, at step 503, the ECU100 records the hydraulic pressures of the rear wheel side hydraulic cylinders 20RL and 20RR detected by the pressure sensor 90 in the memory.

After the process of step 503 is completed, the ECU100 proceeds to step 504, and switches the control valves 61RL and 61RR from the open state to the closed state at time t8, for example, as shown in fig. 6 and 7.

The ECU100 having finished the process of step 504 proceeds to step 505 to determine whether or not the hydraulic pressures of the rear wheel side hydraulic cylinders 20RL and 20RR are equal to or higher than the threshold hydraulic pressure Thop stored in the memory.

If the determination in step 505 is "yes", the ECU100 proceeds to step 506. In other words, for example, when a heavy load is stored in the luggage room, the ECU100 proceeds to step 506.

The ECU100 determines in step 506 whether the vehicle is in a prescribed traveling state. This determination is made based on the detection result of the motion detection sensor 110.

The ECU100 determined as yes in step 506 proceeds to step 507. As shown in fig. 6, for example, at time t9, the ECU100 closes the spring switching valves 62FL and 62FR corresponding to the front wheels WFL and WFR, respectively.

At this time, the ECU100 keeps the spring switching valves 62RL and 62RR corresponding to the rear wheels WRL and WRR in the open state.

If the ECU100 determines yes in

steps

505 and 506, the predetermined high-pressure-time valve switching condition is satisfied. Also, the control that the ECU100 executes in step 507 is referred to as specific valve control.

If the ECU100 executes the specific valve control when the valve switching condition at the time of high pressure is established, the suspension rigidity of the front wheels WFL, WFR is set to be large, and the suspension rigidity of the rear wheels WRL, WRR is set (maintained) to be small. Therefore, the rolling rigidity on the rear wheel WRL, WRR side is not larger than the rolling rigidity on the front wheel WFL, WFR side.

Therefore, for example, when the vehicle is running while turning, the possibility that the steering characteristic of the vehicle becomes oversteer is low.

The ECU100 having finished the process of step 507 temporarily ends the process of this routine.

As shown in fig. 6, if it is determined as no at step 506 of the processing of the present routine next and later, for example, at time t10, ECU100 proceeds to step 510. For example, when the vehicle is running straight at time t10, the ECU100 proceeds to step 510.

Then, the ECU100 opens the spring switching valves 62FL and 62FR corresponding to the front wheels WFL and WFR, respectively. Then, the ECU100 keeps the spring switching valves 62RL and 62RR corresponding to the rear wheels WRL and WRR in the open state. Therefore, for example, when the vehicle travels straight, the ride quality of the vehicle is improved.

On the other hand, when the ECU100 determines "no" in step 505, the ECU100 proceeds to step 508. In other words, for example, if a heavy load is not stored in the luggage room, the ECU100 proceeds to step 508.

The ECU100 determines in step 508 whether the vehicle is in a prescribed traveling state.

The ECU100 determined as yes in step 508 proceeds to step 509. As shown in fig. 7, for example, at time t9, the ECU100 closes the spring switching valves 62FL and 62FR, and closes the spring switching valves 62RL and 62 RR. Then, the amount of rolling motion of the vehicle in the predetermined traveling state becomes small.

At this time, since the hydraulic pressures of the rear wheel side hydraulic cylinders 20RL and 20RR are smaller than the threshold hydraulic pressure Thop, the steering characteristic of the vehicle does not become an oversteer characteristic when the vehicle is running while turning, for example.

The ECU100 having finished the process of step 509 once ends the process of this routine.

When it is determined as no at step 508 of the processing of this routine next and later, for example, at time t10 in fig. 7, ECU100 proceeds to step 510. For example, when the vehicle is running straight at time t10, the ECU100 proceeds to step 510.

Then, the ECU100 opens the spring switching valves 62FL, 62FR, and opens the spring switching valves 62RL, 62 RR.

Although the suspension system 1 of the present embodiment has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.

For example, the present invention may be implemented as a first modification shown in fig. 8.

The roll stiffness distribution between the front wheels WFL, WFR and the rear wheels WRL, WRR has a certain correlation with the ratio of the hydraulic pressures of the front wheel cylinders 20FL, 20FR to the hydraulic pressures of the rear wheel cylinders 20RL, 20 RR. That is, when the rear wheel side hydraulic pressure ratio, which is a value obtained by dividing the hydraulic pressure of the rear wheel hydraulic cylinders 20RL and 20RR by the hydraulic pressure of the front wheel hydraulic cylinders 20FL and 20FR, becomes equal to or higher than a predetermined threshold ratio, the tumble stiffness distribution on the rear wheel side may become excessively large.

The threshold hydraulic pressure Thop in the present modification is set to the hydraulic pressures of the rear wheel hydraulic cylinders 20RL and 20RR when the rear wheel side hydraulic pressure ratio becomes the threshold ratio. That is, the threshold hydraulic pressure Thop of the present modification is a variable value that changes in accordance with the hydraulic pressures of the front wheel cylinders 20FL and 20FR and the rear wheel cylinders 20RL and 20 RR.

As described above, the threshold hydraulic pressure Thop is a value determined based on the relationship between the roll stiffness on the front wheels WFL and WFR side and the roll stiffness on the rear wheels WRL and WRR side, and the hydraulic pressures of the front wheel cylinders 20FL and 20FR and the rear wheel cylinders 20RL and 20 RR. Therefore, if the ECU100 executes the suspension stiffness switching control using the threshold hydraulic pressure Thop, the possibility that the behavior of the vehicle becomes unstable when the vehicle is in the prescribed running state is less.

Fig. 8 shows the hydraulic pressures of the front wheel cylinders 20FL and 20FR and the hydraulic pressures of the rear wheel cylinders 20RL and 20RR when two types of loads are applied to the vehicle.

That is, when a heavy load is placed in the luggage room and the occupant is the driver alone, the hydraulic pressure Opfl of the front wheel cylinders 20FL and 20FR is Ipf + Pa, and the hydraulic pressure Opr1 of the rear wheel cylinders 20RL and 20RR is Ipr + Pb. Pa is the hydraulic pressure of the front wheel hydraulic cylinders 20FL and 20FR increased by the load and the driver. On the other hand, Pb is the hydraulic pressure of the rear wheel hydraulic cylinders 20RL and 20RR, which is increased by the load and the driver. Reference numeral Ipf denotes the hydraulic pressure of the front wheel hydraulic cylinders 20FL and 20FR when no load other than the vehicle acts on the vehicle by moving the load and the driver out of the vehicle. Ipr is the hydraulic pressure of the rear wheel hydraulic cylinders 20RL and 20RR when no load other than the vehicle is applied to the vehicle. Further, in the example shown in fig. 8, Ipr + Pb is the threshold hydraulic pressure Thop. In other words, if the total weight of the cargo and the driver changes, the value of Ipr + Pd sometimes becomes inconsistent with the threshold hydraulic pressure Thop.

On the other hand, in the case where a large-weight cargo is placed in the luggage room provided at the rear portion of the vehicle and a plurality of (many) passengers are present in the vehicle, the hydraulic pressure Opf2 of the front wheel hydraulic cylinders 20FL, 20FR is Ipf + Pc, and the hydraulic pressure Opr2 of the rear wheel hydraulic cylinders 20RL, 20RR is Ipr + Pd. Pc is the hydraulic pressure of the front wheel hydraulic cylinders 20FL and 20FR, which increases due to the total weight of the load and the entire passengers. Pd is the hydraulic pressure of the rear wheel hydraulic cylinders 20RL and 20RR which increases due to the total weight of the cargo and the passengers. In the example of fig. 8, Ipr + Pd is the threshold hydraulic pressure Thop. In other words, if the total weight of the cargo and the passengers changes, the value of Ipr + Pd may not match the threshold hydraulic pressure Thop.

As is apparent from fig. 8, when a large-weight load is placed in a luggage room provided at the rear portion of the vehicle and a plurality of (many) occupants are present in the vehicle, the hydraulic pressures of the front-wheel hydraulic cylinders 20FL and 20FR become larger than those in the case where the occupants to be present in the vehicle are only the driver. Therefore, the threshold hydraulic pressure Thop in this case has a larger value than that in the case where the occupant to be in the vehicle is the driver only.

Therefore, for example, in the case where a heavy load is placed in a luggage room provided at the rear portion of the vehicle and a plurality of (many) passengers are present in the vehicle, the hydraulic pressure of the rear wheel hydraulic cylinders 20RL and 20RR is less likely to be greater than the threshold hydraulic pressure Thop, as compared with the case where a heavy load is placed in a luggage room and only a driver is present in the vehicle. In other words, the hydraulic pressure of the rear wheel hydraulic cylinders 20RL and 20RR is greater than the threshold hydraulic pressure Thop only when the total weight of the load and the passengers is considerable. That is, the valve switching condition at high pressure is hard to be satisfied.

In the first modification, the ECU100 cannot execute the suspension rigidity switching control while the automatic vehicle height control is being executed. In other words, in the case where the automatic vehicle height control is being executed, the specific valve control is not executed when the high-pressure-time valve switching condition is satisfied.

However, in the first modification, the high-pressure valve switching condition is difficult to be satisfied. That is, when the automatic vehicle height control is being executed, it is difficult to set a state in which the specific valve control should be executed.

Therefore, although the specific valve control is not executed in the automatic vehicle height control, for example, when the automatic vehicle height control is being executed in a vehicle that is running while turning, it is possible to reduce the possibility that the steering characteristic of the vehicle becomes an oversteer characteristic.

The present invention may be implemented as a second modification shown in fig. 9.

In the second modification, the suspension system 1 is configured such that the ECU100 can execute the suspension stiffness switching control while the automatic vehicle height control is being executed.

That is, when the valve switching condition is established at the time of high pressure while the automatic body-height control is being executed, the ECU100 executes the specific valve control and interrupts the automatic body-height control.

The flowchart of fig. 9 is the same as the flowchart of fig. 5 except for

steps

901, 902, 903, 909, 910, 915, and 916.

First, the ECU100 determines in step 901 whether or not at least one of the side door and the trunk door is in an open state at the present time.

If the determination in step 901 is yes, the ECU100 proceeds to step 914.

Then, the ECU100 having finished the process of step 914 temporarily ends the process of this routine.

On the other hand, if no is determined in step 901, the ECU100 proceeds to step 902 to determine whether or not the automatic vehicle height control is being executed at the present time.

If it is determined as no in step 902, the ECU100 proceeds to step 903 to set the flag to "0". The initial value of the flag is "0".

The ECU100 having finished the processing of step 903 proceeds to step 907 through the processing of steps 904 to 906. The processing of steps 904 to 906 is the same as steps 502 to 504, respectively, of the flowchart of fig. 5.

Further, if the ECU110 determines yes at step 907 and yes at step 908, the routine proceeds to step 909.

Then, the ECU100 determines no in step 909, and proceeds to step 911 to execute the specific valve control.

On the other hand, if it is determined as yes in step 902, the ECU100 proceeds to step 915 to acquire the hydraulic pressures of the rear wheel side hydraulic cylinders 20RL and 20RR measured by the pressure sensor 90.

At this time, since the automatic vehicle height control is being executed, the control valves 61RL and 61RR corresponding to the rear wheels WRL and WRR are both open.

Further, at step 915, the ECU100 records the hydraulic pressures of the rear wheel side hydraulic cylinders 20RL and 20RR detected by the pressure sensor 90 in the memory.

The ECU100, having finished the process of step 915, proceeds to step 916 to set the flag to "1".

The ECU100, which has finished the process of step 916, proceeds to step 907.

Further, if it is determined as yes in step 907 and yes in step 908, the ECU110 proceeds to step 909.

Then, the ECU100 determines yes at step 909 and proceeds to step 910. That is, the ECU100 suspends the automatic vehicle height control.

The ECU100, which has finished the process of step 910, proceeds to step 911 to execute the specific valve control.

The ECU100 having finished the processing of

step

911, 913, or 914 temporarily ends the processing of this routine.

As described above, in the second modification, when the high-pressure time valve switching condition is satisfied while the automatic body height control is being executed, the automatic body height control is prohibited and the specific valve control is executed.

Therefore, for example, when the automatic vehicle height control is executed during turning of the vehicle, the possibility that the steering characteristic of the vehicle becomes the oversteer characteristic can be reduced.

In the above-described embodiment and modifications, the number of gas springs provided corresponding to each hydraulic cylinder 20 is two (the main accumulator 31 and the sub-accumulator 32), but three or more gas springs may be provided corresponding to each hydraulic cylinder 20. For example, a pressure-reducing gas spring for releasing the pressure in the event of an abnormal rise in the pressure of the hydraulic control circuit 50 may be provided so as to be constantly in communication with the hydraulic cylinder 20.

Each bypass passage 53 and each bypass valve 63 may be omitted from the suspension system 1. In this case, the working oil discharged from the working oil supply and discharge device 70 is supplied to each of the sub accumulators 32 by opening the regulating valve 61 and the spring switching valve 62 at the same time.

Description of the reference symbols

1 … suspension system, 10FL, 10FR, 10RL, 10RR … suspension device, 20FL, 20FR … front wheel side hydraulic cylinder, 20RL, 20RR … rear wheel side hydraulic cylinder, 31FL, 31FR, 31RL, 31RR … main accumulator, 32FL, 32FR, 32RL, 32RR … auxiliary accumulator, 62FL, 62FR, 62RL, 62RR … spring switching valve, 64 … main valve, 71 … pump device, 100 … ECU, 125 … vehicle height selection switch, 130 … vehicle height adjustment closing switch, WFL, WFR … front wheel, WRL, WRR … rear wheel.

Claims

1. A suspension system is provided with:

two front wheel hydraulic cylinders which are respectively provided between left and right front wheels of a vehicle and a vehicle body, which extend and contract according to a change in vertical distance between each front wheel and the vehicle body, and which move the vehicle body upward with respect to the front wheels as a hydraulic pressure of hydraulic oil stored inside increases;

two rear wheel hydraulic cylinders which are respectively provided between left and right rear wheels and the vehicle body, which extend and contract according to a change in vertical distance between each rear wheel and the vehicle body, and which move the vehicle body upward relative to the rear wheels as a hydraulic pressure of hydraulic oil stored therein increases;

a hydraulic oil supply unit capable of supplying the hydraulic oil to the front wheel hydraulic cylinder and the rear wheel hydraulic cylinder while adjusting a hydraulic pressure;

four first gas springs provided corresponding to the front wheel hydraulic cylinders and the rear wheel hydraulic cylinders, respectively, and having a first oil chamber that communicates with the front wheel hydraulic cylinders or the rear wheel hydraulic cylinders and is filled with hydraulic oil, and a first gas chamber that is filled with a gas that generates an elastic force;

four second gas springs independent of the first gas spring, provided corresponding to the front wheel hydraulic cylinders and the rear wheel hydraulic cylinders, respectively, and having a second oil chamber that can communicate with the front wheel hydraulic cylinders or the rear wheel hydraulic cylinders and is filled with hydraulic oil, and a second gas chamber filled with gas that generates elastic force;

two front wheel spring switching valves provided in correspondence with the respective front wheel hydraulic cylinders, and capable of switching between a communication permission state in which the second gas spring and the first gas spring corresponding to the same front wheel hydraulic cylinder are connected in series by permitting communication of the hydraulic oil between the front wheel hydraulic cylinder and the second oil chamber that correspond to each other, and a disconnection state in which the communication is disconnected;

two rear wheel spring switching valves provided in correspondence with the respective rear wheel hydraulic cylinders, and capable of switching between a communication permission state in which the second gas spring and the first gas spring corresponding to the same rear wheel hydraulic cylinder are connected in series by permitting communication of the hydraulic oil between the rear wheel hydraulic cylinder and the second oil chamber that correspond to each other, and a disconnection state in which the communication is disconnected;

a rear wheel side hydraulic pressure detection unit that detects a hydraulic pressure of the hydraulic oil of the rear wheel hydraulic cylinder;

a travel state determination unit that determines whether or not the vehicle is in a predetermined travel state; and

a valve control device that switches the front wheel spring switching valve between the communication permission state and the shutoff state and switches the rear wheel spring switching valve between the communication permission state and the shutoff state,

the valve control device is configured such that,

when the hydraulic pressure of the hydraulic fluid of the rear wheel hydraulic cylinder detected by the rear wheel side hydraulic pressure detection means is less than a predetermined threshold hydraulic pressure and the travel state determination means determines that the predetermined travel state is achieved, the front wheel spring switching valve and the rear wheel spring switching valve are set to the cut-off state,

when the hydraulic pressure of the hydraulic fluid of the rear wheel hydraulic cylinder detected by the rear wheel hydraulic pressure detection means is equal to or greater than a predetermined threshold hydraulic pressure and the travel state determination means determines that the vehicle is in the predetermined travel state, a high-pressure valve switching condition is satisfied, and when the high-pressure valve switching condition is satisfied, specific valve control is executed to bring the front wheel spring switching valve into the blocked state and bring the rear wheel spring switching valve into the communication permission state.

2. The suspension system according to claim 1,

a front wheel side hydraulic pressure detection means for detecting a hydraulic pressure of the hydraulic fluid in the front wheel hydraulic cylinder,

a value obtained by dividing the hydraulic pressure of the hydraulic fluid of the rear wheel hydraulic cylinder detected by the rear wheel hydraulic pressure detection means by the hydraulic pressure of the hydraulic fluid of the front wheel hydraulic cylinder detected by the front wheel hydraulic pressure detection means is a rear wheel hydraulic pressure ratio, and the hydraulic pressure of the hydraulic fluid of the rear wheel hydraulic cylinder when the rear wheel hydraulic pressure ratio becomes a predetermined threshold ratio is the threshold hydraulic pressure.

3. The suspension system according to claim 1,